OCaml retry loop with capped exponential backoff

let retry ?(base = 0.05) ?(cap = 2.0) ?(tries = 5) f =
  let delay attempt =
    let d = Float.min cap (base *. (2. ** float_of_int attempt)) in
    d +. Random.float (d *. 0.25) (* jitter avoids synchronized retries *)
  in
  let rec loop attempt =
    match f () with
    | value -> Ok value
    | exception e when attempt >= tries -> Error e
    | exception _ ->
      Unix.sleepf (delay attempt);
      loop (attempt + 1)
  in
  loop 0